This study is an attempt to evaluate the role of effects which produce occult and overt myocardial failure in a clinical setting in patients following coronary by-pass surgery and in patients with a variety of forms of shock and respiratory insufficiency. It includes both clinical and experimental studies on the role of various myocardial preservation techniques in preventing myocardial depression after coronary bypass surgery, and it also includes studies on the determinants and predictors of myocardial ischemia as influencing myocardial adequacy. These latter studies involve a detailed experimental study of the role of coronary venous pressure, osmolality, potassium concentration, myocardial membrane stabilization, and hypothermia in protecting against ischemia, as well as studies of the intra-myocardial electrical indicators of early and reversible myocardial ischemia. Finally, a major effort is being made in the application of time series analysis, the study of continuously monitored physiologic parameters from critically ill patients as a means of determining periodic patterns of stabilization and predictors of instability that may anticipate myocardial and cardiovascular decompensation in the post surgical patient.